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| United States Patent |
5,240,574
|
|
Fub
, et al.
|
August 31, 1993
|
Process for the photochemical production of halogen compounds
Abstract
The present invention provides a process for the photochemical production
of compounds of the general formula:
R--(C.sub.2 R.sub.4 ').sub.n --X
by telomerisation of an alkyl halide R--X as telogen and of an olefin
C.sub.2 R.sub.4 ' as monomer, in which R is an alkyl radical which is not
halogenated or is partly or completely halogenated, R' can in each case be
the same or different and, independently of one another, are hydrogen,
fluorine, chlorine or bromine atoms or unsubstituted or substituted alkyl
or aryl radicals, n is a natural number from 2 to 10 and X is a bromine or
iodine atom, wherein
(1) a reaction mixture is produced which contains the olefin and the alkyl
halide,
(2) this reaction mixture is irradiated with ultra-violet light, the
wavelength of which is from 230 to 350 nm, and
(3) the end product or end products is/are recovered from the reaction
mixture.
| Inventors:
|
Fub; Werner (Garching, DE);
Zhang; Linyang (Hefei, CN);
von Werner; Konrad (Garching/Alz, DE)
|
| Assignee:
|
Hoechst AG (Frankfurt, DE)
|
| Appl. No.:
|
741897 |
| Filed:
|
August 8, 1991 |
Foreign Application Priority Data
| Current U.S. Class: |
204/157.94; 204/157.61; 204/157.63; 570/125; 570/170 |
| Intern'l Class: |
C07B 037/04; C07C 017/20; C07C 019/08 |
| Field of Search: |
204/157.94,157.61,157.63,158.11
570/125,170
|
References Cited
U.S. Patent Documents
| 2875253 | Feb., 1959 | Barnhart et al. | 260/653.
|
| 3699179 | Oct., 1972 | Boyle et al. | 570/241.
|
| 5017718 | May., 1991 | Ojima et al. | 204/157.
|
| 5073651 | Dec., 1991 | Raab | 570/170.
|
| Foreign Patent Documents |
| 2164567 | Jul., 1973 | DE.
| |
| 48025416 | Dec., 1969 | JP.
| |
Other References
Starks, C. M., "Free Radical Telomerization", Academic Press, N.Y., 1974,
pp. 6-13 and 142-153.
|
Primary Examiner: Niebling; John
Assistant Examiner: Bolam; Brian M.
Attorney, Agent or Firm: Nikaido, Marmelstein, Murray & Oram
Claims
We claim:
1. Process for the photochemical production of compounds of the general
formula:
R--(C.sub.2 R.sub.4 ').sub.n --X
by telomerisation of an alkyl halide R--X as telogen and of an olefin
C.sub.2 R.sub.4 ' as monomer, in which R is an alkyl radical which is not
halogenated or is partly or completely halogenated, R' can in each case be
the same or different and, independently of one another, are hydrogen,
fluorine, chlorine or bromine atoms or unsubstituted or substituted alkyl
or aryl radicals, n is a natural number from 2 to 10 and X is a bromine or
iodine atom, wherein
(1) a reaction mixture is produced which contains the olefin and the alkyl
halide,
(2) this reaction mixture is irradiated with ultra-violet light, the
wavelength of which is from 230 to 350 nm, and
(3) the end product or end products is/are recovered from the reaction
mixture.
2. Process according to claim 1, wherein an alkyl bromide R--Br is used a
telogen.
3. Process according to claim 1, wherein a mono- or dibromoperfluoroalkane
is used as telogen.
4. Process according to claim 1, wherein CF.sub.3 Br, C.sub.2 F.sub.5 Br,
BrC.sub.2 F.sub.4 Br, CBr.sub.2 F.sub.2, ClCF.sub.2 CF.sub.2 Br,
(CF.sub.3).sub.2 CFBr, C.sub.8 F.sub.17 Br ot C.sub.6 F.sub.13 Br is used
as telogen.
5. Process according to claim 1, wherein C.sub.2 F.sub.4, C.sub.2 H.sub.4,
C.sub.3 F.sub.6, CF.sub.2 =CFCl or CH.sub.2 =CF.sub.2 is used as olefin.
6. Process according to claim 4, wherein BrC.sub.2 F.sub.4 Br is used as
telogen and C.sub.2 F.sub.4 as olefin.
7. Process according to claim 4, wherein CF.sub.3 Br or C.sub.2 F.sub.5 Br
is used as telogen and C.sub.2 F.sub.4 as olefin.
8. Process according to claim 4, wherein C.sub.8 F.sub.17 Br or C.sub.6
F.sub.13 Br is used as alkyl halide and C.sub.2 H.sub.4 as olefin.
9. Process according to claim 1, wherein there is used a source of
ultra-violet light with high irradiation intensity.
10. Process according to claim 9, wherein a laser is used as source of
ultra-violet light.
11. Process according to claim 10, wherein a KrF laser with a wavelength of
248 nm is used as source of ultra-violet light.
12. Process according to claim 9, wherein an XeCl laser with a wavelength
of 308 nm is used.
13. Process according to claim 1, wherein the reaction is carried out in
the gas phase.
14. Process according to claim 13, wherein the reaction mixture is cycled
in a circulation system with a cold trap for the condensation of
components of the product mixture of low volatility.
15. Process according to claim 1, wherein the reaction is carried out in
the presence of 0.01 to 1% of a perfluorinated diacyl peroxide, referred
to the total mole number of the reaction participants.
16. Process according to claim 1, wherein the reaction is carried out at
0.degree. to 200.degree. C. when the telogen is a bromide and at 0.degree.
to 100.degree. C. when the telogen is an iodide.
17. Process according to claim 16, wherein the reaction is carried out at a
temperature of at least 25.degree. C.
18. The product produced by the process of claim 1 which product has a
higher purity in the as produced condition than would the product of the
reaction of the same reactants carried out under the influence of ultra
violet light which was not restricted to a wave length of 230 to 350 nm.
Description
The present invention is concerned with a process for the photochemical
production of organic halogen compounds by the telomerisation of an alkyl
halide and of one or more olefin units with the avoidance of by-products.
In particular, the present invention is concerned with a process for the
production of perfluoroalkyl bromides.
A large number of methods is already known for the production of
perfluoroalkyl bromides, some of which are given in the following.
Haszeldine (J. Chem. Soc., 1952, pp. 4259-4268) describes a process for the
production of perfluoroalkyl bromides from silver salts of
perfluorocarboxylic acids which are reacted with bromine, a perfluoroalkyl
bromide shortened by one carbon atom thereby being formed.
U.S. Pat. No. 2,658,928 discloses the production of fluorocarbon
monobromides from the corresponding fluorocarbon monohydrogen compounds by
reaction with elementary bromine at 500.degree. to 600.degree. C. The
hydrogen compounds are, in turn, obtained by the reaction of
perfluoroalkanes with elementary hydrogen at 800.degree. to 900.degree. C.
Federal Republic of Germany Patent Specification No. 11 21 598 discloses a
process for the production of perfluoroalkyl bromides wherein a
perfluoroolefin or a halogen-substituted perfluoroolefin is reacted with
bromine trifluoride or bromine pentafluoride and bromine in the presence
of an inert solvent, bromine fluoride thereby being added to the double
bond of the olefin. However, since the addition does not take place
specifically, in the case of this process two isomers always result.
Published Federal Republic of Germany Patent Specification No. 26 29 774
discloses that perfluoroalkyl chlorides can be converted with HBr in the
gas phase at 100.degree. to 500.degree. C. in the presence of various
catalysts, including activated carbon and metal bromides, into the
corresponding perfluoroalkyl bromides.
U.S. Pat. No. 4,222,968 discloses the reaction of perfluorocarboxylic acids
with bromosulphonic acid fluorides at 0.degree. to 50.degree. C., a
perfluoroalkyl bromide, fluorosulphonic acid and carbon dioxide thereby
being formed as reaction products.
As a method of production for perfluoroalkyl bromides, U.S. Pat. No.
4,469,623 discloses the thermal decomposition of perfluoroalkylsulphonyl
bromides which, in turn, can be produced from the corresponding
perfluoroalkylsulphonyl fluorides. According to U.S. Pat. No. 2,732,398,
these compounds can, in turn, be obtained by electrochemical fluorination.
The above-mentioned processes all display the disadvantages that halogens,
hydrogen halides or similar dangerous substances are used as reaction
components and, in addition, in some cases drastic reaction conditions are
necessary.
The so-called telomerisation is a further technique for the production of
organic molecules and especially of alkyl halogen compounds of medium
chain length. This is a polymerisation of olefins (equation 1), which
almost always takes place via radicals, coupled with a chain transfer
reaction (equation 2). With the use of ethylene as an example of an
olefin, the two reactions of the telomerisation are as follows:
R(C.sub.2 H.sub.4).sub.n-1 +C.sub.2 H.sub.4 .fwdarw.R(C.sub.2
H.sub.4).sub.n( 1)
R(C.sub.2 H.sub.4).sub.n +RX.fwdarw.R(C.sub.2 H.sub.4).sub.n X(2)
The starting radical R of the telomerisation results from the telogen R--X,
which is very frequently a halogen compound, in which X can be, for
example, chlorine, bromine or iodine. R can be produced thermally with or
without a radical starter or also photochemically. A detail review of
telomerisation is to be found in Starks, Free radical telomerization, pub.
Academic Press, 1974.
The production of perfluoroalkyl bromides by telomerisation is itself
known. Thus, U.S. Pat. No. 2,875,253 discloses the telomerisation of
perfluoroalkyl bromides or iodides with unsaturated fluorinated compounds
at 0.degree. to 200.degree. C. in the presence of a peroxy catalyst.
Published Federal Republic of Germany Patent Specification No. 24 16 261
discloses the conversion of short-chained perfluoroalkyl bromides in the
gas phase at temperatures of 250.degree. to 500.degree. C. without
catalyst in the presence of glass rings or metal turnings with
tetrafluoroethylene into longer-chained perfluoroalkyl bromides.
However, in the case of the above-described telomerisation processes, a
uniform product is not obtained. On the contrary, there is obtained a
product mixture with a wide molecular weight distribution, the individual
components of which contain a differing number n of olefin units, the
average number n of the olefin units in the product mixture thereby
depending upon the ratio of the velocities of the reaction equations (1)
and (2). The average molecular weight of the telomerisation products can
thus be controlled to a certain extent by the ratio of the concentrations
of olefin to R--X. However, this method comes up against a limit when this
ratio differs too much from the stoichiometric ratio of the olefin to R--X
which is required by the end product.
Furthermore, in the case of usual telomerisation processes, those
by-products also arise which differ from the starter radical R by an
uneven number of CF.sub.2 groups and products which carry a fluorine atom
instead of X, i.e. undesired by-products which additionally reduce the
yield of desired products.
As starter compounds R--X for the telomerisation reaction, in the case of
known processes, there are preferably used iodine compounds, for example
CF.sub.3 I, C.sub.2 F.sub.5 I and IC.sub.2 F.sub.4 I, since these
compounds can enter very easily into telomerisation reactions with
olefins, for example ethylene or tetrafluoroethylene (see Starks, supra).
The reaction can be initiated thermally or photochemically. The products
thereby resulting can be converted into a large number of other products,
for example:
RC.sub.2 H.sub.4 I.fwdarw.RC.sub.2 H.sub.4 OH (3)
RC.sub.2 H.sub.4 I.fwdarw.R--CH.dbd.CH.sub.2 .fwdarw.R--COOH(4)
2RI+Zn.fwdarw.R.sub.2 +ZnI.sub.2 ( 5)
RI+Hal.sub.2 .fwdarw.RHal+Hal-I (Hal=Br, Cl, F) (6).
However, the use of iodine compounds also gives rise to disadvantages which
are due to the relatively high price, the initiation of corrosion due to
the accompanying decomposition product iodine and the toxicity of some
compounds, for example IC.sub.2 F.sub.4 I. These disadvantages could be
avoided if, instead of the iodine compounds, it were possible to use the
corresponding bromine compounds since a decomposition to bromine
practically does not occur. Furthermore, reaction (6) has the disadvantage
that the handling of the there-mentioned halogens in comparatively large
amounts is difficult and dangerous and is subject to the hazard
regulations. If, however, a bromide is used as starting material, reaction
(6) would be unnecessary insofar as a bromide, for example a
perfluoroalkyl bromide, is desired as product.
However, alkyl bromides as starting material R--X are not very reactive at
20.degree. C., especially for the chain transfer reaction in equation (2).
Thus, in the case of the telomerisation, there preferably result high
molecular weight, wax-like polymers. In the case of comparatively high
reaction temperatures, the average molecular weight of the product mixture
is admittedly smaller but many by-products result. Therefore, because of
these problems, the direct telomerisation of R--Br with a perfluorinated
olefin, for example tetrafluoroethylene, is, in practice, not used for the
production of perfluoroalkyl bromides.
Thus, it is an object of the present invention to provide a process which
at least partly overcomes the disadvantages of the prior art. In
particular, it is an object of the present invention to provide a process
in which is obtained an increased yield of the desired products with the
widest possible avoidance of by-products.
According to the present invention, there is thus provided a process for
the photochemical production of compounds of the general formula:
R--(C.sub.2 R.sub.4 ').sub.n --X
by telomerisation of an alkyl halide R--X as telogen and of an olefin
C.sub.2 R.sub.4 ' as monomer, in which R is an alkyl radical which is not
halogenated or is partly or completely halogenated, R' can be the same or
different and, independently of one another, are hydrogen, fluorine,
chlorine or bromine atoms or unsubstituted or substituted alkyl or aryl
radicals, n is a natural number from 2 to 10 and X is a bromine or iodine
atom, wherein
(1) a reaction mixture is produced which contains the olefin and the alkyl
halide,
(2) this reaction mixture is irradiated with ultra-violet light, the
wavelength of which is from 230 to 350 nm,
(3) the end product or end products is/are recovered from the reaction
mixture.
In the process according to the present invention, an alkyl halide R--X is
used as telogen, i.e. as radical former. X can be an iodine or bromine
atom and is preferably a bromine atom. R can be an alkyl radical which is
not halogenated or is partly or completely halogenated and preferably
contains up to 12 and more preferably up to 8 carbon atoms. Examples for
R--X include CF.sub.3 X, C.sub.2 F.sub.5 X, XC.sub.2 F.sub.4 X, CH.sub.3
X, CX.sub.2 F.sub.2, ClCF.sub.2 CF.sub.2 X, (CF.sub.3).sub.2 CFX and also
larger molecules, such as C.sub.8 F.sub.17 X and C.sub.6 F.sub.13 X. R is
preferably a perhalogenated alkyl radical and especially preferably a
perfluorinated alkyl radical or an alkyl radical which is substituted with
a bromine, chlorine or iodine atom but is otherwise completely substituted
with fluorine atoms. Especially preferred as telogens for the process
according to the present invention are CF.sub.3 Br, C.sub.2 F.sub.5 Br,
BrC.sub.2 F.sub.4 Br, CBr.sub.2 F.sub.2, ClCF.sub.2 CF.sub.2 Br,
(CF.sub.3).sub.2 CFBr, C.sub.8 F.sub.17 Br and C.sub.6 F.sub.13 Br, the
most preferred compounds being CF.sub.3 Br, C.sub.2 F.sub.5 Br and
BrC.sub.2 F.sub.4 Br.
The olefin used as monomer in the process according to the present
invention has the general formula:
C.sub.2 R'.sub.4
In each case, R' can be the same or different and, independently of one
another, are hydrogen, fluorine, chlorine or bromine atoms or
unsubstituted or substituted alkyl or aryl radicals. Preferred examples
for olefins which can be used for the process according to the present
invention include C.sub.2 F.sub.4, C.sub.3 F.sub.6, C.sub.2 H.sub.4,
CF.sub.2 =CFCl and CH.sub.2 =CF.sub.2. Quite generally, olefins are
especially suitable which are accessible to radical polymerisation and are
volatile since the process according to the present invention is
preferably carried out in the gas phase. Perfluorinated olefins are
preferred and especially tetrafluoroethylene. In the process according to
the present invention, it is also possible to use two different monomers,
for example ethylene and tetrafluoroethylene.
The number of olefin units in the end product n is preferably from 2 to 10.
Since the composition of the product mixture produced in the process
according to the present invention also depends upon the concentration
ratio of alkyl halide to olefin, this ratio will be chosen according to
the desired end product. Thus, a higher alkyl halide concentration and/or
a lower olefin concentration must be used when a product is desired of
small chain length, i.e. small n.
The reaction according to the present invention is preferably carried out
in the gas phase. The pressure used is upwardly limited by the vapour
pressure of the bromide or iodide and by the requirement that the olefin
is not to be used in large excess in order not to let the molecular weight
become too great. The total pressure of the reaction components is
preferably from 10 mbar to 2 bar (1 kPa to 200 kPa).
However, the process according to the present invention can also be carried
out in liquid phase, possible in solution. Solvents can thereby be used
which do not react or scarcely react with radicals and which do not absorb
substantially at the wavelength of the irradiation. Examples of solvents
which can be used include n-octane, cyclohexane, CFCl.sub.2 -CF.sub.2 Cl,
acetonitrile, tert.-butanol and CF.sub.3 C.sub.6 H.sub.5 or C.sub.6
F.sub.13 C.sub.6 H.sub.5 (the latter two only in the case of irradiation
wavelengths greater than 300 nm). Non-polar solvents, including the
starting bromide or iodide, thereby increase the proportion of higher
telomerisation products, whereas polar solvents and especially
tert.-butanol and acetonitrile lower the average molecular weight of the
telomerisation products.
As sources of ultra-violet light, in principle there can be used all light
sources which emit ultra-violet light in the wavelength range suitable
according to the present invention. In particular, light sources with high
intensity are preferred since an increase of the intensity or irradiation
surprisingly brings about a reduction of the proportion of high molecular
weight by-products in the reaction product mixture. Thus, for the process
according to the present invention, there is preferably used a laser, for
example a KrF laser (wavelength 248 nm). As light source there can also be
used an XeCl laser (wavelength 308 nm), namely, especially for starting
compounds R--X in which X is an iodine atom, as well as for the liquid
phase where the greater wavelength results in a greater penetration depth.
However, a low pressure mercury lamp (main emission line 253.7 nm) can also
be used when the 184.9 nm line is filtered away, for example with a type
of quartz glass which is unsuitable for vacuum UV, such as Heralux, or
with a liquid such as methanol or glycol which can simultaneously also
serve as cooling medium for the lamp. Use can also be made of high
pressure mercury lamps (particularly the emission band with a maximum at
246 nm) in combination with one or more filters for short-waved
Ultra-violet light (below 230 nm). An Xe short arc lamp in combination
with a filter which is substantially non transparent for ultra-violet
light with a wavelength below 230 nm can also be used.
For the filtering out of undesired wavelengths of the ultra-violet light,
it is preferred to use, besides the already-mentioned filters, especially
dielectric mirrors with a reflection range of 248 .+-.15 nm (usual as
laser mirrors) and, somewhat less good because of transmission losses,
band pass filters which are available in many variants, for example in
combination with mercury lamps.
The ultra-violet light suitable for the process according to the present
invention is to have a wavelength of from 230 to 350 nm. Surprisingly, it
has been ascertained that in the case of irradiation of the reaction
mixture with an unfiltered source of ultra-violet light which emits
irradiation with a wavelength below 230 nm, there always occurs a certain
proportion of undesired by-products with an uneven carbon number, i.e.
instead of a complete olefin unit C.sub.2 F.sub.4, the product only
contains one CF.sub.2 group, or occurs with fluorine instead of bromine.
The formation of these undesired by-products can be avoided when,
according to the process of the present invention, the shortwave part of
the ultra-violet light below 230 nm is filtered off. Furthermore, it has
been ascertained that, in the case of a bromide as telogen, an especially
preferably useable range of the source of ultra-violet light lies between
230 and 270 nm and, in the case of an iodide as telogen, lies between 230
and 350 nm, whereby, however, depending upon the halide used, this range
can also be somewhat narrower or broader. A wavelength of 250.+-.15 nm has
proved to be especially favourable for the process according to the
present invention.
After ending of the telomerisation reaction according to the present
invention, the desired end product or products is/are separated from the
reaction mixture. The separation of the reaction mixture and the
purification of the products can thereby take place in a usual and known
manner, for example especially by fractional distillation, extraction,
fractional precipitation and/or by chromatographic methods.
Furthermore, it has been ascertained that the intensity of the irradiation
has an influence of the average molecular weight of the product mixture.
In the case of higher irradiation intensities, shorter chain lengths are
found than in the case of lower irradiation intensities. This can
naturally be utilised for increasing the yield for a desired product in a
particular process. Thus, in the case of irradiation of a 1:1 gas phase
mixture of BrC.sub.2 F.sub.4 Br and C.sub.2 F.sub.4 (total pressure 200
mbar) with a KrF laser (wavelength 248 nm, pulse length 20 ns) with an
energy density of 10 mJ/cm.sup.2, it is found that the resultant
telomerisation product consists of up 90% of Br(C.sub.2 F.sub.4).sub.2 Br.
In the case of irradiation of the same mixture with radiation between 230
and 270 nm (filter) from a 1 kW xenon short arc lamp, concentrated to an
intensity of 0.3 W/cm.sup.2 on the entry window of the irradiation cell,
there results, on the other hand, a product mixture with a higher average
chain length consisting of Br(C.sub.2 F.sub.4).sub.n Br with 37% n=2, 25%
n=3, 18% n=4 and 12% n=5. Furthermore, if the same starting mixture is
used but a low pressure mercury immersion lamp with 0.1 W/cm.sup.2
radiation strength at 253.7 nm on the surface, besides the above products
there are already found 5% of wax-like polymers.
The average molecular weight was reduced in a similar manner when the
absorbed energy is increased by choice of a wavelength which is more
strongly absorbed. Thus, in the case of irradiation of BrC.sub.2 F.sub.4
Br+C.sub.2 F.sub.4 (in each case 200 mbar) with a XeCl laser (wavelength
308 nm, weak absorption), wax-like polymers are observed, whereas in the
case of irradiation with a KrF laser (248 nm, about 1000 times stronger
absorption), in the case of the same laser energy the main product was
BrC.sub.4 F.sub.8 Br.
In the case of the process according to the present invention, it has
proved to be especially favourable to carry out the reaction in a gas
phase and, during the reaction, to cycle the mixture of reactants and
products in a circulating system with a cold trap. The temperature of the
cold trap is thereby so chosen that the desired end product condenses out,
whereas the more volatile components of the reaction mixture are again
returned to the radiation zone. In this way, it is achieved that, after a
few circulations, the products have a substantially uniform molecular
weight. This means that the desired product can be obtained in very high
yield. If, for example, the telomerisation of BrC.sub.2 F.sub.4 Br and
C.sub.2 F.sub.4 is carried out as above with the use of a 1 kw Xenon short
arc lamp as source of ultraviolet light (irradiation wave length between
230 and 270 nm) but with a reduction of the C.sub.2 F.sub.4 pressure by a
half (to 50 mbar), adding repeatedly 50 mbar C.sub.2 F.sub.4 thereto, if
necessary, i.e. with progressive reaction, and circulating the product
mixture between the irradiation cell and a cold trap at 5.degree. C.,
then, in the case of almost complete reaction, there is obtained a mixture
of 45% each of Br(C.sub.2 F.sub.4).sub.2 Br and of Br(C.sub.2
F.sub.4).sub.3 Br, the last mentioned compound thereby forming 82% of the
end products which are not again returned into the irradiation zone by the
circulating system.
In the case of the process according to the present invention, a radical
starter compound can possibly also be present. As radical starters, there
can be used perfluorinated diacyl peroxides, for example
bis-(trifluoroacetyl) peroxide or bis-(pentafluoropropionyl) peroxide. The
concentration of these radical formers can be in the range of from 0.01 to
1%, referred to the total mole number of the reaction participants.
The reaction temperature lies substantially below the temperature at which
the reaction proceeds spontaneously; thus in the case of bromides below
400.degree. C. and in the case of iodides below 150.degree. C. However, it
is also preferably above 0.degree. C. Especially preferably, in the case
of bromides it is from 25.degree. to 200.degree. C. and in the case of
iodides from 25.degree. to 100.degree. C.
A series of valuable compounds can be produced with the process according
to the present invention. Thus, for example,
.alpha.,.omega.-dihaloperfluoroalkanes of the type X(CF.sub.2
CF.sub.2).sub.n X, in which X is an iodine or bromine atom and n is
preferably 3 or 4, are valuable intermediates for the synthesis of
.alpha.,.omega.-difunctional compounds, such as dicarboxylic acids, diols,
dienes and the like. According to the present invention, such compounds
can be obtained by the telomerisation of BrC.sub.2 F.sub.4 Br and C.sub.2
F.sub.4. An exchange of X for chlorine or fluorine or a coupling of the
end products, for example a reaction of the iodides with zinc in acetic
anhydride, gives inert liquids or inert waxes: thus, for example, C.sub.16
F.sub.34 is a special ski wax.
Perfluoroalkyl bromides, for example C.sub.6 F.sub.13 Br, C.sub.8 F.sub.17
Br, C.sub.9 F.sub.19 Br, BrC.sub.6 F.sub.12 Br, find a further use as
X-ray contrast agents not only in blood vessels but also, for example, in
the intestines, as ultrasonic contrast agents, as oxygen carriers and for
fluorine nuclear magnetic resonance tomography for the recognition and
combating of cancer and cancer cells. However, of most importance is the
use of mono- and dibromoperfluoroalkanes with vapour pressures of 5 to 50
mbar as blood replacement materials. Such compounds can be produced
purposefully and with substantial avoidance of by-products from CF.sub.3
Br, BrC.sub.2 F.sub.4 Br or C.sub.2 F.sub.5 Br and C.sub.2 F.sub.4.
The following Examples are given for the purpose of illustrating the
present invention, reference being made to the accompanying drawings in
which:
FIG. 1 shows the product composition in the case of irradiation of
BrC.sub.2 F.sub.4 Br+C.sub.2 F.sub.4 with a Xe short arc lamp in
dependence upon the initial composition,
FIG. 2 shows the product composition of the same system as in FIG. 1 in
dependence upon the intensity of irradiation,
FIG. 3 shows the same system as in FIG. 1 with the use of a circulation
system in dependence upon the period of irradiation,
FIG. 4 shows the product composition in the case of irradiation of
BrC.sub.2 F.sub.4 Br+C.sub.2 F.sub.4 with a low pressure mercury lamp with
and without gas circulation,
FIG. 5 shows the same system as in FIG. 4 without (below) and with (above)
filter, and
FIG. 6 shows the product composition in the case of irradiation of
BrC.sub.2 F.sub.4 Br+C.sub.2 F.sub.4 with a KrF laser without gas
circulation.
EXAMPLE 1
Irradiation with a Xe short arc lamp.
For the irradiation of a reaction mixture consisting of C.sub.2 F.sub.4
+BrC.sub.2 F.sub.4 Br with a Xe short arc lamp (Osram XBO 1000
watt/HS.OFR) or with a high pressure mercury lamp (Osram HBO 500 watt/2),
there was used a cylindrical irradiation cell of 10 cm. length and 3.6 cm.
diameter with windows of quartz glass. The reaction temperature was
25.degree. C.
The cell has two gas connections. In the case of the circulation of the
gas, as gas entry there was used the connection close to the irradiation
window in order to flush away depositions which, under circumstances,
arise. Besides the irradiation cell, the circulation system also contains
a cold trap and a circulation pump (Brey, TFK1M, oil-free vane-type rotary
pump with graphite rotor) which was operated with a speed of 0.2 1/sec.
The lamps were operated with a mains supply and a housing (Amko A 5001)
which had a focussing mirror with 20 cm. focal distance and f number 2.5.
For the high pressure lamps, there was used a dielectric mirror which
reflected more than 90% of the light between 233 and 263 nm, whereas the
reflection for the other wavelengths lay substantially below 5%.
The products were analysed gas chromatographically in combination with a
mass spectrometer. As column there was used a 0.2 mm. * 25 mm. capillary
which was coated with 5% phenylmethylsilicone. Temperature programme: 2
min. 30.degree. C., then with 5 K/min. to 200.degree. C. For the mass
spectrometer sensitivity (total ionic current of mass 23 to 800), there
was taken the group additivity: The relative signal of several calibration
compounds can be well represented as the sum of contributions of 0.25,
0.40, 1.00 and 1.10 of the groups Br, CF.sub.3, C.sub.2 H.sub.4 and
C.sub.2 F.sub.4, respectively.
FIGS. 1 to 3 show the product compositions under different reaction
conditions. FIG. 1 demonstrates the influence of the concentration ratio
halide/olefin. Conversion and associated quantum yields were, with
increasing olefin pressure, 11% and 0.7, 12% and 1.7, 15 and 2.1 or 7% and
2.1.
FIG. 2 shows the influence of the irradiation intensity. The initial
pressures for halide and olefin were, in each case, 200 mbar. The
parameters on the curves give the ultraviolet power (230 to 270 nm) on the
entry window of the irradiation cell. The conversion of the bromide
amounted to between 9% (0.13 W) and 14% (0.76 W). The associated quantum
yield was 2 to 2.3. In the case of the experiments illustrated in FIGS. 1
and 2, the circulation system was not used and the conversion of the
initial bromide kept low (0 to 15%).
On the other hand, FIG. 3 shows the product compositions with increasing
conversion of the bromide (up to 96%) in the case of circulation with cold
trap (5.degree. C.) and with repeated making up of C.sub.2 F.sub.4
according to the measure of the consumption, i.e. of the pressure drop.
The irradiation time is interrelated with the irradiation energy (both
plotted on the oblique coordinates) via the irradiation power (0.27 watt
in the UV). The height of the first bar (at time point 0) corresponds to
100% of the starting bromide and gives the scale for the vertical
coordinate (composition). The bromide initial pressure amounted to 100
mbar and the olefin addition to 4.times.65 mbar. The conversion of the
bromide amounted to 96% and the associated quantum yield to 0.7.
EXAMPLE 2
Irradiation with a low pressure mercury lamp
In the experiments with the low pressure mercury lamp, there was used an
immersion lamp Heraeus TNN 15/32 (15 W electrical, 3 W UV, 0.1 W/cm.sup.2
on the surface). For the absorption of the 185 nm line, methanol (layer
thickness 3 mm.) was filled into its protective mantle. The lamp was
dipped into a 4.5 liter three-necked flask, the two other necks of which
were connected with the circulation system (see Example 1). The starting
mixture consisted of 100 mbar BrC.sub.2 F.sub.4 Br+20 mbar C.sub.2
F.sub.4. The two gases were supplemented according to the amount of
consumption. In total, the amount of starting material was 20 g. As liquid
products, in total there were obtained 12.5 g. The conversion of the
bromide amounted to 68 and 74%, respectively. In FIG. 4, there is given
the product composition without gas circulation as a solid line and with
gas circulation as a broken line. In the case of the use of circulation,
the reduction of the high molecular weight products can clearly be seen.
In comparison with the Xe lamp, the products which result in the case of
the use of the low pressure mercury lamp as ultra-violet source contain
one more C.sub.2 F.sub.4 unit.
FIG. 5 shows the difference of the product composition with and without
methanol filter. Here, a small quartz cell (65 ml.) was illuminated
externally, without gas circulation and with a conversion of the bromide
of 38 or 51% with or without methanol, respectively. No monobromides and
no uneven carbon numbers were observed with methanol as filter. The
initial pressure of the bromide was 100 mbar. The olefin was added in
three portions (50+48+28 mbar) according to the amount of consumption. In
both cases, the irradiation time was 15 minutes.
EXAMPLE 3
Irradiation with a KrF laser
In the case of the experiments with a KrF laser (Lambdaphysik EMG 102), the
cell and the circulation system of Example 1 were used. The laser energy
on the entry window was 40 mJ/pulse in the case of a pulse period of 20
ns. The beam cross-section was 2.8 cm.sup.2.
FIG. 6 shows some examples of the product composition after irradiation of
BrC.sub.2 F.sub.4 Br+C.sub.2 F.sub.4 in the case of about 33% conversion
of the bromide without gas circulation. The statement of 4.times.50 mbar
C.sub.2 F.sub.4 in the case of the dotted curve means that the olefin was
added in 4 portions according to the amount of consumption. The conversion
of the bromide and the associated quantum yields were, in the case of the
unbroken curve, of the broken-line curve and of the dotted line curve, 20%
and 1.8, 32% and 1.6 and 72% and 0.7, respectively. Independently of the
composition of the starting mixture, the product BrC.sub.4 F.sub.8 Br
always predominated by far (85-93%).
EXAMPLE 4
Further telomerisation experiments were carried out with a KrF laser, the
laser and the irradiation cell being as in Example 3. Irradiation was
carried out up to 15% conversion of the bromide in each case. The
circulation system was not used.
In the case of irradiation of 200 mbar CF.sub.3 Br+400 mbar C.sub.2
H.sub.4, there result 93% CF.sub.3 C.sub.2 H.sub.4 Br, 3.2% CF.sub.3
C.sub.4 H.sub.8 CF.sub.3 and 2.5% CF.sub.3 C.sub.4 H.sub.8 Br. With 25
instead of 400 mbar C.sub.2 H.sub.4, there are obtained 94% CF.sub.3
C.sub.2 H.sub.4 Br, 1.5% CF.sub.3 C.sub.4 H.sub.8 CF.sub.3 and about 4%
C.sub.2 F.sub.6.
The telomerisation of C.sub.2 F.sub.5 Br and C.sub.2 H.sub.4 showed
precisely corresponding results.
In the case of irradiation of 200 mbar BrC.sub.2 F.sub.4 Br+400 mbar
C.sub.2 H.sub.4 with 90 mJ and 4 mJ pulses of a KrF laser, respectively,
there were obtained the following product compositions:
______________________________________
laser energy 90 mJ 4 mJ
______________________________________
BrC.sub.2 F.sub.4 C.sub.2 H.sub.4 Br
47% 33.8%
BrC.sub.2 F.sub.4 C.sub.4 H.sub.8 C.sub.2 F.sub.4 Br
20.7% 42.3%
BrC.sub.2 F.sub.4 C.sub.2 H.sub.4 C.sub.2 F.sub.4 Br
16.0 3.8%
BrC.sub.4 F.sub.8 Br 7.8% 3.6%
BrC.sub.2 F.sub.4 C.sub.4 H.sub.8 Br
3.1% 6.3%
BrC.sub.2 F.sub.4 C.sub.2 H.sub.3
2.5% 5.1%
BrC.sub.2 F.sub.4 C.sub.2 H.sub.5
2.5% 5.1%
quantum yield of the main product
1.4 4.5
______________________________________
If 125 mbar C.sub.2 F.sub.4 are additionally added to the reaction mixture
(laser 20 mJ), then BrC.sub.2 F.sub.4 C.sub.4 H.sub.8 C.sub.2 F.sub.4 Br
results with a quantum yield of 93 and a selectivity of 78%.
From 6 mbar BrC.sub.2 F.sub.4 C.sub.2 H.sub.4 Br+100 mbar C.sub.2 H.sub.4,
there result in the case of 25 mJ laser energy:
______________________________________
BrC.sub.2 H.sub.4 C.sub.2 F.sub.4 C.sub.2 H.sub.4 Br
60% (quantum yield 0.4)
BrC.sub.2 F.sub.4 C.sub.4 H.sub.8 C.sub.2 F.sub.4 Br
30%
BrC.sub.2 F.sub.4 C.sub.4 H.sub.8 C.sub.2 F.sub.4 C.sub.2 H.sub.4
6.5%
BrC.sub.2 F.sub.4 C.sub.4 H.sub.8 Br
3.5%
______________________________________
With much lower irradiation intensities such as, for example from a mercury
low pressure lamp, the main product is BrC.sub.2 F.sub.4 C.sub.4 H.sub.8
Br.
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